The present disclosure is directed to a circuit for a hydraulic pump and, more particularly, to a drain prevention circuit for a hydraulic pump.
Hydraulic pumps are commonly used for many purposes in many different applications. Vehicles, such as, for example, highway trucks and off-highway work machines, commonly include hydraulic pumps that are driven by an engine in the vehicle to generate a flow of pressurized fluid. The pressurized fluid may be used for any of a number of purposes during the operation of the vehicle. A highway truck, for example, may use pressurized fluid to operate a fuel injection system or a braking system. A work machine, for example, may use pressurized fluid to propel the machine around a work site or to move a work implement.
A hydraulic pump typically draws fluid from a reservoir and applies work to the fluid to increase the pressure of the fluid. The hydraulic pump may direct the pressurized fluid into a fluid rail or another supply system. The hydraulic pump may be configured to vary the amount of pressurized fluid that is directed into the fluid rail. This may be accomplished with a variable displacement pump or with a fixed displacement pump that has a variable flow.
A typical hydraulic pump includes a control mechanism that governs the operation of the pump. The control mechanism may, for example, control the displacement of the pump, the flow rate of the pump, the output pressure of the pump, or the horsepower or torque input to the pump. As described in U.S. Pat. No. 5,567,123 to Childress et al., these types of control mechanisms may use pressurized fluid that is generated during the operation of the hydraulic pump as an input. This may be accomplished by returning a portion of the pressurized fluid generated by the pump to the control mechanism.
When, however, the pump is stopped, such as when the engine of the vehicle is shut off, the connection between the output of the hydraulic pump and the control mechanism can allow some fluid to escape from the fluid rail. The escaping fluid may allow for the formation of air pockets within the fluid rail. This may be a more significant problem when the hydraulic pump is mounted in a position where the pump is physically lower than the fluid rail. When the engine and hydraulic pump are re-started, the hydraulic pump will have to force the air from the fluid rail before the hydraulic system will operate as expected. In certain applications, such as, for example, in a fuel injection system, this can cause difficulty in starting the engine.
The hydraulic pump circuit of the present disclosure solves one or more of the problems set forth above.
According to one aspect, the present disclosure is directed to a hydraulic pump that includes a housing having a fluid inlet and a fluid outlet. A pumping element is operable to increase the pressure of fluid received through the fluid inlet and to generate a flow of pressurized fluid through the fluid outlet. A control device is operatively engaged with the pumping element to control the flow rate of the flow of pressurized fluid generated by the pumping element. A fluid passageway connects the control device with the fluid outlet. A valve is disposed in the fluid passageway between the fluid outlet and the control valve. The valve is moveable between a first position where the valve blocks a flow of fluid relative to the fluid passageway and a second position where a flow of fluid is allowed to flow through the fluid passageway.
In another aspect, the present disclosure is directed to a method of operating a hydraulic pump. A pumping element is operated to increase the pressure of a fluid and generate a flow of pressurized fluid to a fluid rail. A control device is adjusted to control the flow rate of the flow of pressurized fluid to the fluid rail. A portion of the flow of pressurized fluid generated by the pumping element is directed to the control device. A valve is closed to prevent the portion of the flow of pressurized fluid from flowing to the control device when the pressure of the fluid in the fluid rail is below a predetermined limit.